1. Field of the Invention
The present invention relates to an ink-jet printer driver in which electrostriction elements are caused to press ink to jet out of nozzles so as to form characters/graphics with ink dot matrices.
2. Description of the Prior Art
Referring to FIGS. 11(a) through 11(e), construction of part of a head of an ink-jet printer according to the present invention will be described. In these figures, reference numeral 1 designates a nozzle plate having a nozzle 1a, 2 designates an elastic plate, 3 designates liquid ink, and 4 designates an electrostriction element which is distorted by an electric field. The electrostriction element is closely attached on the elastic plate 2.
FIG. 11(a) shows a standby condition in which the elastic plate 2 is projected toward ink by the distortion of the electrostriction element 4. FIGS. 11(b) through 11(d) show the steps in which the elastic plate 2 is recovered to its neutral point by gradually removing the electric field from the electrostriction element 4, respectively.
FIG. 11(e) shows a condition in which an electric field is suddenly applied to the electrostriction element 4 to make the elastic plate 2 project toward the ink 3 to thereby jet the ink 3 outward. If the application of the electric field is continued as it is, the head returns to its standby condition, as shown in FIG. 11(a).
In an alternative ink jetting method, the electrostriction element 4 is provided within the ink. The present invention is applied to both the methods.
A printer head is constituted by combining a plurality of aforementioned constructions. In the case of a serial printer, the number of the constructions is from 8 to 64. In the case of a page printer, the number of the constructions is from 1400 to 4000.
A conventional art for driving the aforementioned printer head is shown in FIGS. 12 and 13. In FIG. 12, reference numeral 5 designates a high-voltage electric source which, in general, has an output voltage V.sub.o within a range of from 50 to 200 V. The output voltage may vary in accordance with the characteristics of constituent parts due to the response frequency. Symbol TR.sub.S represents a P-type transistor for switching a voltage V.sub.o so as to feed a signal V.sub.x to the printer head. Reference numeral 6.sub.i designates one driving circuit.
In the driving circuit 6.sub.i, an electrostriction element 7.sub.i is charged to a voltage V.sub.0 through a resistor R.sub.3i having a value of several M.OMEGA., so that the situation is returned to the aforementioned standby state. A diode D.sub.i for isolating the driving circuit from other driving circuits and a resistor R.sub.1i serve to charge the electrostriction element 7.sub.i rapidly. When an N-type transistor TR.sub.Di is turned on, the charge of the electrostriction element 7.sub.i is absorbed through a resistor R.sub.2i having a larger resistance value than that of the resistor R.sub.1i, so that the voltage drops as shown in the point A in FIG. 13(b). The symbol i attached to the driving circuit 6.sub.i, the electrostriction element 7.sub.i, and other parts in the driving circuit 6.sub.i are used to show those parts or components representatively because a plurality of such driving circuits are provided respectively for a plurality of printer heads as described above.
Reference numeral 8 designates a driving signal generating means which serves to give a switching signal to the transistor TR.sub.S periodically. A driving signal is given to the transistor TR.sub.Di in accordance with existence of a dot forming instruction. FIG. 13(a) shows a state of the transistor TR.sub.S for performing a switching operation periodically.
In the case where the charge of the electrostriction element 7.sub.i has been absorbed, the electrostriction element 7.sub.i is charged rapidly through the diode D.sub.i and the resistor R.sub.1i during the ON-state of the transistor TR.sub.i so that ink is jetted as shown in FIG. 11(e). On the contrary, in the case where the electrostriction element 7.sub.i has been charged to a value of V.sub.0, the charged voltage of the electrostriction element 7.sub.i does not change so that ink is not jetted.
The resistance value of the resistor R.sub.1i is selected to be several k.OMEGA. and the charging time constant is selected to be a value in a range of from 5 to 10 .mu.s so as to prevent occurrence of wasteful ink jetting caused by overshooting of the elastic plate 2.
The resistance value of the resistor R.sub.2i is selected to be of the order of several tens of k.OMEGA. and the charging time constant is selected to be a value within a range of from 20 to 100 .mu.s so as to prevent occurrence of both wasteful ink jetting caused by an undercoat and air suction from nozzles. If air is sucked into ink, it becomes impossible to perform ink jetting only by contraction of air.
The equivalent capacitance of the electrostriction element 7.sub.i is within a range of from 100 to 1000 PF.
The foregoing is that related to a conventional ink-jet printer driver.
In the aforementioned prior art, however, there arises a problem in that elements having accurate values are required because a driving circuit 6.sub.i is constituted by resistors R.sub.1i, R.sub.2i, R.sub.3i and a diode D.sub.i to obtain a driving waveform as shown in FIG. 13(b). Further, there arises another problem in that the degree of freedom cannot be obtained because the rising and falling characteristics are fixed. Furthermore, there arises a further problem in that an exact time constant is required making it difficult to prepare the circuits in the form of ICs, and, accordingly, assembling cost becomes high though the constituent parts or elements per se are inexpensive in cost.
In particular, as the number of nozzles is increased to 24, 64, . . . 3000, or in other words, the capacity of the printer is increased, the aforementioned problems become serious. On occasion, there may arise a defect in that assembly becomes impossible.